The UK's Ambassador in Turkey has faced questions over reports that GCHQ organised surveillance of the country's delegation to an international summit in London.

The Turkish foreign affairs ministry raised the issue with Sir David Reddaway in a phone call, the Foreign Office said. Britain's electronic eavesdropping agency is alleged to have mounted an intensive spying operation on foreign politicians attending two G20 summit meetings in London in 2009.

The reports have the potential to embarrass the Prime Minister as he hosts leaders from the world's most powerful countries at the G8 summit in Northern Ireland - the biggest gathering of international statesmen to take place in the UK since the London G20.

A Foreign Office spokesman confirmed that the Turkish government had raised the allegations with Sir David, but insisted he had not been summoned to answer questions in person. A spokeswoman said: "I can confirm that the Turkish Ministry of Foreign Affairs raised the issue with the Ambassador. It was discussed in a phone call. He was not summoned."

The Prime Minister refused to answer questions on the row as world leaders arrived for the G8 summit at Lough Erne in Northern Ireland.

The Guardian said leaked documents show that in 2009 delegates had their computers monitored and phones intercepted on the orders of the British Government. The intelligence agencies were even said to have set up internet cafes specifically to enable them to read the emails of those taking part in the summit.

Asked whether he could guarantee his guests that no similar operation was in place at Lough Erne, David Cameron told Sky News: "We never comment on security or intelligence issues and I am not about to start now. I don't make comments on security or intelligence issues - that would be breaking something that no government has previously done."

According to The Guardian the Turkish finance minister - and possibly 15 other members of his party - were among those targeted in 2009. The newspaper said the documents suggested that the 2009 operation was sanctioned at a senior level in the government of then prime minister Gordon Brown and that the intelligence obtained was passed to ministers.

Details of the eavesdropping were contained in documents obtained by Edward Snowden, the US National Security Agency (NSA) whistle-blower responsible for a string of disclosures about US intelligence operations.

GCHQ previously said in relation to an earlier report about its involvement in NSA operations that its work was carried out "in accordance with a strict legal and policy framework which ensures that our activities are authorised, necessary and proportionate".